The printing speeds in laser printers and copiers that use electrophotographic systems have been undergoing dramatic increases in recent years. This has created demand for toners that exhibit better durabilities and better low-temperature fixabilities. In particular, low-temperature fixability, in view of its connection to reducing power consumption, has come to be an essential requirement in toner development in recent years given the strong demands on toner development for environmental responsiveness.
In addition, as the market for laser printers and copiers has grown broader, the requirement has arisen that the toner be stable and exhibit its properties even when stored in a high temperature environment. Moreover, the elimination of fans from the interior of image-forming apparatuses in pursuit of smaller and quieter image-forming apparatuses has resulted in increasingly elevated temperatures within image-forming apparatuses. As a consequence, a high storage stability under even higher temperatures has come to be required of toner.
Given this background, there have been investigations of toners that have a so-called core-shell structure, in which, in order to satisfy the low-temperature fixability, the core is formed of a binder resin that encompasses a wax and, in order to satisfy the requirements for a high development durability and a high storage stability, the shell is formed of a resin that has a high glass-transition temperature or a resin that has a high molecular weight.
For example, with the objects of achieving oilless fixing and improving the transmissiveness of OHT images, Patent Document 1 discloses a suspension polymerized toner that encompasses an ester wax.
With the object of improving the developing performance, transfer performance, and fixing performance of toner, Patent Document 2 discloses a wax-encompassing toner comprising a styrene-butyl acrylate copolymer core coated with a shell of a styrene-methacrylic acid-methyl methacrylate copolymer.
[Patent Document 1] Japanese Patent Application Laid-open No. H8-050367    [Patent Document 2] WO 2008/126865